U.S. Pat. No. 5,505,072 (hereinafter the No. '072 patent), which is assigned to the assignee of the current application, describes a scanning circuit for a pressure responsive array. Such arrays typically utilize two layers, each of which has a parallel array of electrodes formed thereon with the electrodes for at least one of the arrays being covered with a variable resistance pressure sensitive ink or other pressure sensitive material, which arrays are secured together with the electrodes of one layer crossing the electrodes of the other layer to form pressure points. By sensing the current passing through each pressure point, and thus the resistance thereat, the pressure at the point may be determined.
The circuit of the No. '072 patent provides a number of improvements over prior art sensing circuitry for such arrays, and in particular provides a mechanism for controlling the sensitivity of the array, and thus its dynamic range, by both varying an applied test voltage and providing a reference voltage which varies depending on desired sensitivity to control the circuit output. While the circuit of the No. '072 patent functions very well to perform its sensitivity control and other functions, the circuit requires a fair amount of hardware to perform these functions and is therefore not suitable for some applications of such sensors, including some applications where the array consists of a single pressure point, where very inexpensive sensors are required. A need therefore exists for a pressure sensor output circuit which provides sensitivity control and dynamic range which is at least as good as that for the circuit of the No. '072 patent, but at significantly lower cost.